Vehicle brake systems are generally equipped with a device for detecting a braking intention. A variable control force is externally applicable to these braking-intention detection devices, which then convert the control force into a correlating actuation travel. For this purpose, braking-intention detection devices normally have a brake master cylinder which a driver is able to operate with the aid of a brake pedal or a brake lever.
Vehicle brake systems forming the basis of the present invention are furthermore equipped with an electromechanical brake booster, which executes an actuation travel as a function of the actuation travel of the braking-intention detection device via a first electronic control device in order to boost the brake pressure generated by the driver.
In this context, an existing travel sensor system supplies a travel signal that correlates with the actuation travel of the braking-intention detection device to the first electronic control device. For this purpose, known travel sensors may be equipped with an absolute travel sensor or, as an alternative, with a differential travel sensor. While an absolute travel sensor is used for measuring the actuation travel of the braking-intention detection device, a differential-travel sensor measures the actuation travel of the braking-intention detection device relative to the actuation travel of the electronic brake booster, and thus measures a travel difference between the two devices.
In addition, vehicle brake systems that form the basis of the present invention are also equipped with an electronic brake-pressure control device. It adapts the brake pressure of the individual wheel brakes to the slip conditions of the respectively allocated wheels of the vehicle. The brake-pressure control device is equipped with a second electronic control device for this purpose, which, in addition to valves that may be acted upon electronically, controls a pressure generator able to be driven by an electric motor. Depending on the function scope, vehicle brake systems having such brake-pressure control devices are also known under the terms ABS, ASR or ESP vehicle brake systems.
A data bus connection or a communications link is available between the first electronic control device of the brake booster and the second electronic control device of the brake-pressure control device, via which a first signal, which represents the operativeness of the brake boosting, and a second signal, which represents the actuation of the braking-intention detection device, are able to be transmitted. This second signal may be a binary trigger signal, which is set when a driver has exceeded a specifiable actuation threshold, e.g., a minimum actuation travel of the braking-intention detection device.
In certain vehicle brake systems, during a state of an existing function interruption of the brake boosting, this brake boosting is alternatively assumed by the pressure generator of the brake-pressure control device. An actuation signal for the pressure generator is supplied by the allocated second electronic control device. A method for calculating this actuation signal is described in the earlier patent application DE 10 2016 225 694. This method is based on the described binary trigger signal, which is offset against a signal that considers the system or brake pressure generated in the brake-pressure control system by the actuation of the braking-intention detection device.
In this context it is disadvantageous that the binary trigger signal has to be transmitted to the second electronic control device of the brake-pressure control device via a discrete connection line because a transmission of this trigger signal via the communications link between the first electronic control device of the brake booster and the second electronic control device of the brake-pressure control device is no longer possible. The reason for this is that a status signal is superimposed onto the trigger signal, which sets the status of the trigger signal from currently “signal valid” to “signal invalid” when an interruption has been detected at the electronic brake booster. That is to say, the described method is used even when the travel signal from the braking-intention detection device is still available since the components for the generation and the transmission of this travel signal continue to be operational. For example, the latter case may arise when an exclusively mechanical fault exists at the brake booster but the electronic system is still functional; when a deactivation of the electronic brake booster takes place due to a detected rise in temperature or due to an excessive vehicle system voltage or a vehicle system voltage that is too low; or when the trigger event is a fault that occurred when a data memory in which, for example, the function status of the brake booster is stored is read out.